In the UK, the Road
Vehicles Lighting Regulations 1989 (Statutory Instrument 1989 No 1796)
govern the installation, performance and use of all vehicle lighting.
The following paragraphs outline some of the basic rules.

Position lamps

Drivers must use front and rear position
lamps (parking and taillamps) between sunset and sunrise and at other
times in conditions of seriously reduced visibility, defined in the
Highway Code as being, generally, less than 100 metres.

Headlamp Use Requirements

Drivers must use dipped (low) beam headlamps during the "hours of
darkness" (half an hour after sunset till half an hour before sunrise)
except on certain well lit roads ie: roads where the street lights are
less than 185 metres (600 ft) apart. Drivers must also used dipped beam
headlamps in conditions of seriously reduced visibility.Headlamps must not
cause undue dazzle or discomfort to other road users and must not be lit
when a vehicle is parked.

Headlamps must be kept clean and in good working order. However,
a vehicle with a defective headlamp between sunrise and sunset is not
committing an offence if the lamp became defective during the journey or
if it will be repaired "with all reasonable expedition".

European Union Situation

Within the European Union, Directive 76/756 EEC, as last amended by
91/663/EEC, governs the installation of lighting and light signalling
devices. All EU Member States must permit the entry into service of
vehicles which comply with this Directive. Compliance with 76/756 as
amended effectively became mandatory starting 1 January 1996 throughout
the EU for new M1-class vehicles (essentially passenger cars) subject to
EC Whole Vehicle Type Approval.

Dim-dip Requirements

The UK Road Vehicle Lighting Regulations require vehicles first used on or
after 1st April 1987 to be fitted with a dim-dip device or running lamps
unless they fully comply with the lighting installation Directive. Dim-dip
devices must provide an intensity of between 10 and 20% of the intensity
of the normal dipped beam. Running lamps must provide an intensity of more
than 200 candelas directly in front of the lamps and parallel to the
longitudinal axis of the vehicle, and less than 800 candelas in any
direction.

Dim-dip History

At the 18th Sessional Meeting of the Commission Internationale de
l'Eclairage (CIE) in London in 1975, a joint committee concerned with
visual signalling, road lighting and automobile lighting came to the
following conclusion:

It is recommended that a 'town beam' be introduced which is
intermediate in intensity between that of the currently used low beam and
side lights. Such a light should have a luminous intensity between 50 and
100 cd and should have an area similar to that of current headlights.
Therefore it is recommended that all relevant organisations
consider this matter seriously and take the necessary steps to introduce a
town beam as an essential part of the lighting systems for road
traffic.

The committee believed such a beam would provide conspicuous and glare
free front lighting on vehicles. They suggested the beam could be simply
realized by using the existing dipped beam headlamp on a lower
voltage.

The UK was the only country to introduce a dim-dip system. The simplest
such system merely consists of a relay and a 0.5 to 1 ohm resistor. This
causes the dipped headlamps to light up automatically at reduced intensity
whenever the engine and the side lights are switched on. Side lights can
still be used on their own when parking, and dipped headlamps for any
roads at night when they are necessary to illuminate the road.

In 1980, in response to Parliamentary pressure about the advantages of
headlamps or side lights in towns, the Minister of Transport decided to
consult interested parties about the implementation of the dim-dip system
as described above.

Following strong support from the public and professional bodies eg:
Association of Chief Police Officers, ROSPA, Institution of Public
Lighting Engineers, with the exception of the motor industry itself, the
Minister made regulations in 1983 bringing in the dim-dip requirement for
all cars, buses and trucks first used after 1st April 1987. As an
alternative to using dim-dip, a pair of special large, bright front
position lamps were permitted, as requested by some vehicle manufacturers,
but none have as yet made use of this option.

In 1976 the EC made a special Directive covering the installation of lamps
on vehicles (76/756/EEC). The Articles made it clear that Member States
must permit free circulation and sale of any vehicle which conformed to
the directive in respect of the lighting devices listed and covered by
detailed provisions.

The dim-dip device, together with the daytime running lamp and side
marker lamp were not so listed, so the UK took the view that, although
the directive had successfully standardized the installation of all common
vehicle lamps, it did not prohibit a Member State from requiring other
devices not listed in the directive.

This view was reinforced by the fact that the side marker lamp had been
required by UK law for many years without challenge, and the CIE statement
recommending "relevant organisations" to take the necessary steps to
implement the town beam had also not been challenged.

The EC Commission sought technical advice from GTB on the value of
dim-dip. GTB recommended against dim-dip or town lights and recommended
instead in favour of mandatory use of dipped headlights in towns at night.
The EC Commission did not take advice from road lighting experts, nor from
CIE. The EC Commission believed that having consulted GTB they had taken
the advice of CIE as the sole relevant expert authority on the subject of
vehicle front lights for lit streets.

On the basis of GTB's technical advice, the Commission prosecuted the UK
in the European Court of Justice. The 1988 Decision favoured the
Commission on the grounds that they, the Commission, had intended the
vehicle lighting directive to cover all vehicle lighting devices and
therefore any device not listed in the directive could not be required by
a Member State to be fitted.

When the Decision was announced, the UK amended its regulations to permit,
instead of a dim-dip device, either a special daytime running lamp or full
compliance with the EC directive including, in particular, the
requirements in respect of accurate headlamp alignment.